High frequency power combiner/divider

ABSTRACT

Radio frequency (RF) power amplifiers are provided which may include high power, wideband, microwave or millimeter-wave solid state power amplifiers based on waveguide power combiner/dividers.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/726,073 filed on Dec. 22, 2012, now U.S. Pat. No. 9,065,163, whichclaims the benefit of priority of U.S. Provisional Application No.61/580,100, filed on Dec. 23, 2011, the entire contents of whichapplications are incorporated herein by reference.

GOVERNMENT LICENSE RIGHTS

This invention was made with government support under contract number#FA8650-11-C-1159 awarded by U.S. Air Force. The government has certainrights in the invention.

FIELD OF THE INVENTION

The present invention relates generally to radio frequency (RF) poweramplifiers, and more particularly but not exclusively to high power,wideband, microwave or millimeter-wave solid state power amplifiersbased on waveguide power combiner/dividers.

BACKGROUND OF THE INVENTION

Current high power microwave amplifier applications usually employtravelling wave tubes (TWT) to provide microwave power magnification.However, the drawbacks of TWT amplifiers are significant, such asconsiderable size and weight. Further, TWT amplifiers require a highvoltage driver, such as an electronic power conditioner, that in turnnecessitates additional complex accessory circuits and involves highvoltage risk. To work linearly, TWT amplifiers are normally backed offfrom their saturated output power or additional linearization circuitsare added, and linearization circuitry usually results in a dramaticincrease in the system complexity and cost. In addition, vacuum tubes,including TWT's, typically require operation at a designed output power;however, atmospheric variation may require a source that can change itspower level based on conditions in the transmit/receive path. Thisinevitable variability can often lead to running an amplifier either attoo high or too low of a power level for the conditions at hand and canlead to unnecessarily high levels of power consumption. Furthermore,often power amplifiers are required to feed systems that demandcontinuous operation without substantial interruption, and therefore mayrequire a back-up to be ready and waiting in the event of failure of theprimary amplifier. Due to the long warm-up times of vacuum tubes, oftenan identical tube or power supply needs to be idling in the event offailure of the first tube, further degrading the ability to meet demandsfor small size, weight, and power efficiency as is often needed forcommunications satellites, mobile ground stations, radar systems, andother applications especially those supporting mobile, airborne, andspace environments.

Alternatively, a solid state power amplifier (SSPA) module forsatellite, terrestrial, aerospace, and/or unmanned aerial vehicle (UAV)applications may require compact size and light weight. Further, suchapplications may require an SSPA module that has more power than onemonolithic microwave integrated circuit (MMIC) chip can provide. TheSSPA continues to advance into the territory traditionally dominated bythe vacuum tube amplifier in terms of increased frequency, power, andbandwidth as the MMIC chips to support them continue to advance, forexample with advances in GaN and GaAs semiconductor technology. Thereare various ways to power combine MMICs into a higher power SSPAassembly. Existing SSPA designs are based on power combiners, such asradial combiners, but they sometimes tend to be bulky, heavy, and/orrequire complex machining. In an effort to reduce this complexity, suchwaveguide components are sometimes made in two parts that are assembled,often called a “split block”. Even though split block waveguidestructure/combiners can be used to reduce machining complexity, the SSPAmay suffer from both leakage problems and joining problems. This problemof building a waveguide from separate parts that must be joined, andgeneral insertion and return loss problems over the bandwidth required,can be compounded or increased by the tolerances and structural accuracyneeded to properly guide the propagating waves in a hollow waveguideconstruction. For example, to minimize the insertion loss and returnloss, integration of conductive signal line based waveguides, such asmicrostrip, CPW (Co-Planar Waveguide), or coax, with hollow waveguidesis additionally complicated due to tolerances and alignment that may berequired. Because a high power SSPA usually has high loop gain, the RFleakage of a multi-part or traditional combiner system could severelydegrade the system performance. In addition, existing SSPA designs maybe difficult to manufacture at high frequency, for example at V-band andW-band, and their size and weight may increase the cost of launching asatellite into orbit or make UAV (Unmanned Aerospace Vehicle)applications impossible.

One difficulty faced by previous SSPA designs is that they do not workwell at high frequencies. Commonly used components, such as stripline,microstrip line, coax, splitter and combiner structures, all includeparasitic effects and may suffer material/substrate loss. Higherfrequency signals may be significantly attenuated when passing throughthese structures. Parasitic effects of interconnections, splitters,combiner structures, and/or the materials used to propagate the signalmay contribute to the frequency limitations inherent with the SSPAdesigns in the art. As frequency increases, the tolerances and accuracybetween the electromagnetically critical elements within the passivecombining and feed structures become increasingly sensitive to error andso methods of construction that work well at several or several 10's ofGHz are unsuitable for obtaining high performance at 40, 60, 90, 180, or240 GHz.

SSPA designs may include a large number of components that must bemanually assembled and tuned after assembly. Many individual pieces ofexisting SSPA designs require complex machining, such as, for example,extremely high precision milling, wire Electric Discharge Machining(EDM) and/or laser processes which lead to relatively high manufacturingcosts and challenges in the part integration and bonding to produce adevice with sufficiently good electromagnetic properties, for example,in terms of accumulative insertion and/or return loss. Additionally, insome circumstances, required machining tolerances at high frequenciesmake mass production difficult because every SSPA may have to bemanually assembled and tuned to compensate for the manufacturingtolerances. Accordingly, there may be a need for a solid state highpower amplifier module which has more desirable cost, size, precisionforming, precision assembly, and/or reliability attributes and thatreadily lends itself to scalable, and cost-effective, manufacturingmethods.

SUMMARY OF THE INVENTION

In one of its aspects the present invention may relate to a microwave ormillimeter-wave solid state high power amplifier such as those that areused in radar and satellite communication systems. An exemplarywaveguide device configuration may contain at least one port to accept atransmission line mode of at least one signal line and to convert it toat least one hollow core waveguide mode within at least one hollow corewaveguide combiner. The hollow core waveguide combiner may include oneor more branching sections that divide or combine electromagneticsignals, which sections may meet to divide or combine energy and powerfrom two hollow core waveguide branches. Exemplary devices may includeprecision electrical and/or mechanical features for the conversionbetween a transmission line mode and hollow waveguide radiation mode(s).

For example, in an exemplary configuration a waveguide powercombiner/divider of the present invention may include a plurality ofhollow waveguides having a hollow core configured to support at leastone radiation mode therein. The waveguides may include first and secondends with the second ends in communication with one another to permitcommunication of radiation modes therebetween. The second ends may bejoined in way to allow or form a common output port for the 2 or morewaveguide first ends. A plurality of transmission line waveguides havinga center conductor transmission line disposed therein may also beprovided. Each of the transmission line waveguides, for example coaxialtransmission line waveguides, may include an electromagnetic endlauncher operably connected to respective first ends of the hollowwaveguides. Each electromagnetic end launcher may include an elongatedcenter conductor end portion that extends into the hollow core of thehollow waveguide. In addition, a plurality of ground posts may also beprovided, each of which may be disposed at a respective end launcher inelectrical communication with the center conductor and a wall of thehollow waveguide to ground the end launcher to the hollow waveguidewall.

The electrical and/or mechanical features, particularly those thatrequire precision spatial alignment and/or 3D spatial relationships toeach other, may be formed in a build sequence monolithically ordirectly, for example using an additive microfabrication process, suchas the PolyStrata® process by Nuvotronics, LLC. As taught in thisinvention disclosure, by using such methods, the later alignment andassembly for transition between a plurality of signal line ortransmission line based waveguides, said electromagnetic end launchers,and hollow core waveguides is not required. In such a case theserelationships are determined image-wise, for example by application ofsuccessive planar photo-patterns or precision machine defined patterns.In this regard, in a further of its aspects the present invention mayprovide a novel power combining structure based on a microfabricationprocess which permits the precision manufacturing of small parts,typically on a wafer, substrate, grid-level, or batch level. Otherprecision forming techniques such as, for example, precision milling,stereolithography, solid printing, or injection molding, may be used tocreate either all, or a part of, the novel power combining structuresdisclosed herein.

In exemplary configurations, power combining structures of the presentinvention may include an air-coax input power divider; pre-driver,driver, sub-amplifier modules (which may themselves include an air-coaxdivider and combiner, phase shifters, filters and/or linearizers), amicrofabricated output waveguide combiner; and/or, an air-coax orwaveguide output. The power amplifier may be made in a modular formatallowing building blocks that can be independently tested and which aidin scalable products that reuse similar or identical components in theirarchitecture. In exemplary configurations, the relationships for themechanical elements which govern the electromagnetic properties may beaddressed during the forming process. Likewise, precision integration ofthese components may allow them to be assembled with the necessarytolerances and precision for an intended application.

In exemplary configurations, the waveguide combiner portion of the SSPAmay be fed by a number of amplifier modules (or “sub-modules”) feedingeach input port and the respective input port end launcher of saidhollow core waveguide power combiner. Each of these amplifier modulesmay have multiple MMIC chips (e.g., such as 2 chips, 4 chips or 8 chipsusing a 2-way or 4-way or 8-way Wilkinson or Gysel sub-combiner). Suchcombiners as the Wilkinson or Gysel can provide higher isolation than ahollow waveguide combiner alone, for example, and can provide isolationamong MMIC chips. This can help provide graceful degradation in theevent of any partial or individual chip failures of the overallcombining performance. For example, with an 8-way radial hollowwaveguide power combiner, 32 or 64 MMIC chips may be combined togetherwhen fed by eight 4-way or 8-way micro-coaxial power combiningsub-modules. In other configurations, 4-way, 8-way, 10-way, or N-wayradial combiners can be used, and additional or fewer MMIC chips may becombined together. Thus the overall SSPA may be improved by combiningthe port protection and isolation of 2 or more chips combined using a 2or n-way Wilkinson or Gysel, each of which modules feed an input port ofthe hollow core waveguide combiner. Thereby the SSPA is benefited by thelow loss of hollow core waveguide combining and the port to portisolation of a transmission line combiner.

In another of its aspects, the present invention may enable precisionformation of waveguide devices. For example, the structures of thepresent invention, such as the combining waveguide structure, may bebuilt using a microfabrication process or another precisionmanufacturing technique, such as, for example, precision milling,stereolithography, electrochemical forming, chemical or photochemicaletching, EDM machining, solid printing, deep RIE, stamping, LIGA, lasersolidification or powders or liquids, laser machining, casting,PolyStrata® processing, transfer molding, or injection molding.Depending on the frequency of operation the waveguide combiner can befabricated as a reduced height waveguide or as a full height waveguideat higher frequency (e.g., about 1 mm at V-band). In FIGS. 1A-15B, thecombining waveguide structure may have such a reduced height dependingon the frequency. Because of the ability to reduce the waveguide height,the size and weight of the combiner may be significantly minimized atlower frequency where large waveguide are needed. Since power combiningmay be within either air-coax and/or a waveguide combiner/divider, theSSPA or system overall loss may be lower than other designs.Furthermore, as the manufacturing tolerances may be in the micron range,the phase error may be further reduced so that the efficiency of theSSPA may be significantly improved. Several parameters in the combinersuch as the end launcher 100 are very sensitive to fabricationtolerances particularly at extremely high frequency, mm wave and sub-mmwave. Fabrication precision and accuracy in this novel approach can aswell keep the low loss combining performance up to such high frequencies(e.g., from 30 GHz to 300 GHz and can be applied up to 1 THz).

In a further aspect, the present invention may include a electromagneticend launcher to provide conversion of an RF transmission line mode, suchas coax, to/from a hollow waveguide radiation mode, which may haverelatively low loss and increased ease of fabrication. Such anelectromagnetic end launcher may be integrated directly into thewaveguide manufacturing process to prevent alignment and bonding errors,whereas prior designs may have used independently fabricated, aligned,and tuned and bonded E-probes for coax to waveguide transition. (In suchE-probe designs, the non-air-coax structure may cause higher loss athigh frequencies, such as at the Ka-, V- and W-bands.) Additionally, acoax or air-coax to waveguide end launchers may be microfabricatedmonolithically with the microfabricated waveguide combiner to provideenhanced manufacturing control and/or enhanced performance. Moreover,alignment features and/or precision mechanical interlocks that enableprecision registration and/or connection of such launchers, and/orMMICs, and/or connectors and/or E-probes may be incorporated into theformation process to enable precision integration and assembly of suchparts with precision in the tolerances and the electrical, mechanical,thermal, and/or electromagnetic connections between them.

An added benefit of the electromagnetic end launcher designs that aregrounded is the mechanical stability of such structures to vibration andthermal and mechanical shock. Having an end of the electromagnetic endlauncher, or a region near an end of the electromagnetic end launcherformed, fused, adhered, or mechanically attached to a hollow waveguidewall region can suppress or prevent vibrations, oscillations, andprovides stability for the geometric relations in a highly fixed manner.Eliminating such vibrations of the launcher while it is exposed tovibration or shock can prevent phase noise and other degradation of theamplified signal quality when said SSPA is exposed to such environmentswhich are often encountered in aerospace and mobile terrestrialapplications. This is particularly important when the environment formounting or housing the SSPA is subject to severe vibrations andaccelerations as may be found in a moving vehicle such as helicopter,jet, car, tank, or rocket. When formed through a multi-layermicrofabrication build process such as PolyStrata®, such metalstructures may be formed layer by layer. However, it should be clear asdescribed in the PolyStrata® processes that metal could also be affixedor adhered to a defined region of dielectric such as a dielectricpedestal. The shapes and materials can be optimized using design andoptimization software such as HFSS™ produced by Ansoft.

Exemplary configurations of the present invention may include one ormultiple sub-modules each of which typically includes multiple MMICchips. The sub-module may be tested separately before final assemblyand/or may be replaced or repaired. All of the MMIC chips in asub-module may be placed on a common heat sink for improved heatdissipation. Also such sub-module amplifiers may be similarly bonded toregions in or on a common planar thermal heat sink or ground plane. FIG.15A shows an example of this architecture where modules 1514 or 1614,the waveguide power combiner 800, the input divider 1516 could all beplaced onto on a common heatsink. The SSPA 1500 shows an example of sucharchitecture, where the thermal management will be greatly enhance,improving weight, power consumption and longer term reliability to namea few. Removing the heat primarily down and out from one primary planesimplifies the housing and mounting requirements of the SSPA system andallows the areas above and around the plane to be used for interconnectsand other components. Such an approach may produce a substantially morecompact amplifier design than, for example, a more traditional radialwaveguide approach, and may also simplify the supporting structures,such as the thermal management support. Such planar launchers andcombiners may help reduce the number of layers and/or height and/orthickness required to produce the assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary and the following detailed description ofexemplary embodiments of the present invention may be further understoodwhen read in conjunction with the appended drawings, in which:

FIGS. 1A-1C schematically illustrate perspective and side elevationviews, respectively, of an exemplary electromagnetic end launcher inaccordance with the present invention for transitioning between atransmission line mode and hollow waveguide radiation mode, with thehollow waveguide shown in phantom;

FIGS. 2A-2B illustrate the simulated performance for the electromagneticend launcher of FIGS. 1A-1C for the reflection coefficient S(1,1) andinsertion loss S(2,1), respectively;

FIGS. 3A-3B illustrate the simulated performance for the hollowwaveguide and electromagnetic end launcher of FIGS. 1A-1C for thereflection coefficient S(1,1) as a function of ground post width W1 andlength L3;

FIG. 3C illustrates the simulated performance for the hollow waveguideand electromagnetic end launcher of FIGS. 1A-1C for the insertion lossS(2,1) as a function of hollow waveguide height;

FIGS. 4A-4B schematically illustrate perspective views of two additionalexemplary electromagnetic end launchers in accordance with the presentinvention for transitioning between a transmission line mode and hollowwaveguide radiation mode, with the hollow waveguide shown in phantom;

FIGS. 5A-5B schematically illustrate perspective views of exemplary4-way waveguide power combiner/dividers in accordance with the presentinvention which incorporate the electromagnetic end launcher of FIGS.1A-1C, with the hollow waveguide combiners shown in phantom;

FIGS. 6A-6F illustrate the simulated performance for the powercombiner/divider of FIG. 5B in terms of S-parameters over a range offrequencies when optimized for two different center frequencies (60 and73 GHz respectively);

FIG. 7A schematically illustrates a perspective view of an exemplary8-way waveguide portion of a waveguide power combiner/divider inaccordance with the present invention;

FIGS. 7B-7D illustrate the simulated performance at E band for thewaveguide power combiner/divider of FIG. 7A in terms of S-parameters,where the eight ports associated with the electromagnetic end launchersare numbered as ports 2-9 and the center coax port is numbered as port1;

FIGS. 8A-8C schematically illustrate perspective and cross-sectionalviews of an exemplary 8-way waveguide power combiner/divider inaccordance with the present invention which incorporates theelectromagnetic end launcher of FIGS. 1A-1C into the waveguide portionof FIG. 7A;

FIG. 8D illustrates the simulated performance at V-band for thewaveguide power combiner/divider of FIGS. 8A-8C;

FIG. 8E illustrates the simulated effect of ground post position onimpedance match S(2,2) in an 8-way waveguide power combiner/divider ofthe present invention;

FIGS. 9A-9B schematically illustrate perspective views of exemplary10-way and N-way waveguide power combiner/dividers in accordance withthe present invention, respectively, which incorporate theelectromagnetic end launcher of FIGS. 1A-1C;

FIGS. 10A-10B schematically illustrate perspective and side elevationviews, respectively, of an exemplary 2-way waveguide portion of awaveguide power combiner/divider in accordance with the presentinvention, which incorporates two electromagnetic end launchers of FIGS.1A-1C;

FIGS. 11A-11B schematically illustrate perspective views of an exemplary16-way waveguide power combiner/divider in accordance with the presentinvention which incorporates eight 2-way waveguide portions of FIGS.10A-10B;

FIG. 12A schematically illustrates perspective views of the 16-waywaveguide power combiner/divider of FIGS. 11A-11B with a center coaxport further coupled to a hollow waveguide;

FIG. 12B schematically illustrates a perspective view of two 16-waywaveguide power combiner/dividers of FIGS. 11A-11B each having arespective center coax port further coupled to a hollow waveguide;

FIGS. 13A-13B schematically illustrate perspective views of an exemplary8-way waveguide power combiner/divider having an exemplaryelectromagnetic end launcher in accordance with the present invention inwhich the transmission line includes a 90 degree turn external to thehollow waveguide;

FIGS. 14A-14B schematically illustrate perspective views of an exemplary16-way waveguide power combiner/divider having an exemplaryelectromagnetic end launcher similar to that of FIGS. 13A-13B;

FIGS. 15A-15B schematically illustrate perspective views of exemplarysolid state power amplifier (SSPA) implementations of waveguide powercombiner/dividers in accordance with the present invention;

FIG. 16 schematically illustrates a SSPA constructed from a substratewith preamplifiers and a divider network, a waveguide combiner, and MMICpower amplifiers or MMIC power combiner module sub-assemblies, inaccordance with the present invention; and

FIG. 17 schematically illustrates amplifier circuit block diagramsherein used as amplifier module subassemblies or sub-modules showingthat a combiner/divider structure may use cascading 2-way splits tocombine/divide 2 or more, e.g., 4 or 8, channels.

DETAILED DESCRIPTION OF THE INVENTION

In view of the aforementioned needs in the art, in one of its aspectsthe present invention provides waveguide power combiner/dividers whichare designed with the recognition that RF power can be more efficientlycombined/divided when the power is contained in radiation modes ofhollow waveguides rather than in RF signals in transmission lines. (Asused throughout this disclosure, the term “combiner/divider” is used torefer to a device having a structure which can either combine or divideRF power, depending on how the device is incorporated in an overallsystem architecture. For example, if a combiner/divider includes N portsat a first end and a single port at a second end, the combiner/dividermay function as a divider if an input signal is provided to the singleport and divided output signals delivered to the N ports; conversely,the combiner/divider may function as a combiner if input signals areprovided to the N ports and a combined signal is output from the singleport.)

To enable practical use of power combination/division in hollowwaveguide radiation modes within the context of an overall systemarchitecture that typically transmits power in RF transmission lines(i.e., conductors), the present invention provides, in one of itsaspects, an electromagnetic end launcher 100 for converting RF powerto/from RF signals in a transmission line 105 from/to radiation modes ofa hollow waveguide 120, FIG. 1A. Exemplary waveguide powercombiner/dividers 500 in accordance with the present invention may inturn incorporate the electromagnetic end launchers 100 at one or moreinput/output ports of the waveguide power combiner/divider 500, FIG. 5A.Used as a combiner, for example, the waveguide power combiner/divider500 may receive four RF transmission line signals, each input at arespective one of the electromagnetic end launchers 100, which arelaunched into radiation modes in respective hollow waveguide portions200. The launched radiation modes may then combine within the waveguide250, and the combined radiation modes may then be converted back into atransmission line mode at a transmission line output port 330, which maybe provided in the form of an air-coax waveguide having a centerconductor transmission line 310 and waveguide wall 320.

Turning to the electromagnetic end launcher 100 more specifically, andreferring to the figures wherein like elements are numbered alikethroughout, the exemplary electromagnetic end launcher 100 of thepresent invention may include a center conductor transmission line 105which may be provided in the form of a transmission line waveguide 108,such as an air-coax waveguide having an outer coaxial waveguide wall 106with an air dielectric therebetween, for example, FIGS. 1A-1C. Theelectromagnetic end launcher 100 may include a launch end 102 in theform of a longitudinally extended portion of the center conductortransmission line 105 which projects into the hollow cavity of a hollowwaveguide 120 to provide an end launcher 100 in which the transmissionline 105 enters the hollow waveguide 120 parallel to the plane of thehollow waveguide 120 through a waveguide sidewall. Alternativeconfigurations are also possible in which an electromagnetic endlauncher 400, 410 enters a hollow waveguide 420, 430 perpendicular tothe longitudinal axis of the hollow waveguide 420, 430 either through aside surface or an upper surface of the hollow waveguide 420, 430,respectively, FIGS. 4A, 4B. In FIG. 4B the outer conductor of thecoaxial transmission line is not shown protruding above the surface,however it should be clear it would typically follow a similar symmetryas illustrated in FIG. 4A.

Typically, the launch end 102 may be supported within the hollowwaveguide 120 by a ground post 104 in electrical communication with thecenter conductor transmission line 105 and a conductive outer wall 122of the hollow waveguide 120. The ground post 104 may have a rectangularor other suitable shape. In exemplary configurations, it may beparticularly desirable that the ground post 104 be locatedlongitudinally inward from the distal end 103 of the launch end 102 at alocation such that the distal end 103 is suspended to overhang theground post 104, i.e., L3>0, FIG. 1C. While not intending to be bound byany particular theory, it is believed that such an arrangement with L3>0enables broader frequency of operation as well as finer tuning for lowerloss operation, especially as frequency increases from a few 10's of GHzto 100's of GHz. In turn, high performance may be maintained byimproving the return loss and reducing the loss from end launcher towaveguide transition. In addition, parameters believed significant todevice tuning include h1, h2, L1, L2, w1, and W1, FIG. 1B. For example,the length L2 can be optimized to tune the frequency of operationrelative to the height of the ground post 104 (h1) such that the totallength (L2+h1) is optimized to be close to a ¼ of the design wavelengthof the RF signals to be combined/divided. For instance, if theelectromagnetic end launcher 100 is optimized to operate at 60 GHz, thedimensions of L2 and h1 may be 1.0 mm and 0.52 mm, respectively.Similarly, the waveguide width (w1) may be 3.76 mm for a design atV-band and 3 mm for a design at E-band.

The ability to accurately control W1 and L1 is also believed to enablestructures with a larger bandwidth of operation. For instance values ofW1=0.7 mm and L1=0.13 mm are appropriate for use with the aforementionedvalues of L2 and h1. The height of the waveguide cavity h2, e.g., 1 mm,can also be optimized to further improve the insertion loss of theelectromagnetic end launcher 100. For these exemplary values, simulatedperformance of reflection coefficient S(1,1) and insertion loss S(2,1)shows acceptable performance of the electromagnetic end launcher 100 atV and E-band, where the transmission line waveguide 108 is numbered asport 1 and the hollow waveguide 120 is numbered has port 2, FIGS. 2A,2B. From the figures it is seen that reflection at the transmission linewaveguide 108 is less than 18 dB from 70 GHz to 77 GHz, and theinsertion loss from the transmission line waveguide 108 to the hollowwaveguide 120 is less than 0.1 dB from 70 GHz to 77 GHz.

As further evidence of the tuning of the electromagnetic end launcher100 afforded by the dimensional parameters noted above, FIGS. 3A, 3Bsimulate the effect on impedance match as a function of variation in thewidth of the ground post 104. Specifically, for an overhang lengthL3=0.1 mm, a ground post width W1=0.6 mm is seen optimal from 50 GHz to70 GHz, FIG. 3A, and for an overhang length L3=0.17 mm, the ground postwidth W1=0.254 mm is optimal from 60 GHz to 100 GHz. The remainingvalues used in the simulations of FIGS. 3A, 3B were L1=0.127 mm,L2=1.306 mm, h1=0.533 mm, h2=1.016 mm. Additionally, FIG. 3C simulatesthe effect of waveguide height h2 on insertion loss S(2,1). (The effectof overhang length L3 is best illustrated in terms of a complete powercombiner/divider structure e.g., combiner/divider 700, FIG. 7A, and isthus addressed later.) The simulations also demonstrate the need forvery good dimensional control and the advantages of a monolithic ornearly monolithic fabrication. The structures disclosed herein, such aselectromagnetic end launcher 100, waveguide power combiner/divider 800,amplifier modules 1614, or input power divider network 1670 describedbelow, are examples of structures leveraging these advantages. While notall of these elements require monolithic fabrication between each ofthem, there are geometric and mechanical tolerances within each of themthat cannot typically be achieved in common high precision subtractivemachining operations like precision milling. For example in FIG. 8 theperspective see-through and cross-sectional view in FIGS. 8B, 8C showthe connections between the end-launcher, its electromagneticallyshielded feed structure (recta-coaxial in this case), the end launcher100 itself (a grounded probe structure) at a terminal end, and thewaveguide combining structure 750 with waveguides and common combiningarea. There are tolerances and mechanical relationships between theseelements and their dimensions that preferably range from several micronsto 10 microns in the EHF range of frequencies. It can be see that thereare both protruding and recessed areas in the conductive interiorsurface that are shown. Building such an assembly using a largelymonolithic process such as a layer by layer sequential microfabricationprocess such as PolyStrata and/or combining the lower half (the feedstructures and end-launchers in such a process and then combining theupper waveguide combiner using a “sandwich” or clam-shell configurationcan enable such tolerances to be achieved. Preferably, any assembly thatmay be required is done in as few steps as possible so that the requiredtolerances are met to achieve the desired performance.

Returning to FIG. 5A, just as the electromagnetic end launchers 100 mayassume various exemplary configurations, variation in the configurationof the transmission line output port 330 may also be made. For instance,the transmission line output port 330 may be provided in the form of anair coax waveguide having a center conductor 310 which may be suspendedout of contact with the conductive base wall of the waveguide 250.However, such a configuration may have undesirable mechanical stabilitydue to the suspended nature of the center conductor 310. As analternative, a transmission line output port 350 may be provided havinga center conductor 353 which is supported by a cylindrical conductivebase 352 which is in turn disposed on, and supported by, a base wall ofthe hollow waveguide 354. For a waveguide height h2=1 mm, the conductivebase may have a thickness of 0.15 mm and diameter of 0.5 mm. Theperformance of such structures in terms of S-parameters is simulated inFIGS. 6A-6F.

In addition to 4-way waveguide power combiners/dividers 500, a greateror fewer number of waveguide portions 200 with electromagnetic endlaunchers 100 may be provided in waveguide power combiner/dividers ofthe present invention. FIG. 7A, for example, illustrates an 8-waywaveguide combiner 700 prior to fitting with electromagnetic endlaunchers, but including a transmission line output port 730 with centerconductor 710. The width of each waveguide portion 750 may be about 3mm, and the height of the waveguide portion 750 may be about 1 mm atV-band or 3.8 mm at E band. Simulated performance of the 8-way waveguidecombiner 700 is illustrated in FIGS. 7B-7D, where the transmission lineoutput port 730 is numbered as port 1 and the eight waveguide portions750 are numbered as ports 2-9 for purposes of defining the S-parameters.Specifically, FIG. 7B illustrates that the reflection loss at thetransmission line output port 730 is less than 19 dB from 70 GHz to 77GHz; FIG. 7C illustrates that the insertion loss from the transmissionline output port 730 to the waveguide portions 750 is less than 0.1 dBfrom 70 GHz to 77 GHz; and, FIG. 7D illustrates that the phase from thetransmission line output port 732 to the waveguide portions 750 isidentical from 70 GHz to 77 GHz.

The 8-way waveguide combiner 700 may form the basis of an 8-waywaveguide power combiner/divider 800, FIG. 8A-8C, in accordance with thepresent invention with the inclusion, for example, of theelectromagnetic end launchers 100 at each waveguide portion 750 toprovide eight radial feed points, in a manner similar to thatillustrated in FIGS. 1A-1C, 5A. Simulated performance of the 8-waywaveguide power combiner/divider 800 is illustrated in FIG. 8D, wherethe transmission line output port 830 is numbered as port 1 and theeight waveguide portions 750 are numbered as ports 2-9 for purposes ofdefining the S-parameters; the reflection loss at the transmission lineoutput port 830 is less than 20 dB from 70 GHz to 77 GHz. The 8-waywaveguide power combiner/divider 800 also provides a convenientarchitecture for simulating the effect of overhang length L3. Forexample, impedance match S(2,2) may be optimal for L3=0.17 mm from 57GHz to 63 GHz, for L1=0.127 mm, L2=1.306, mm, W1=0.508 mm, h1=0.533 mm,and h2=1.016 mm, FIG. 8E.

In addition to 4-way and 8-way waveguide power combiner/dividers, higherorder exemplary combiner/dividers may be provided by the presentinvention, including a 10-way waveguide power combiner/divider 900 up toan N-way waveguide power combiner/divider 950 each of which may includethe electromagnetic end launchers 100 of FIGS. 1A-1C, for example. Stillhigher orders of combination/division may be provided by incorporatingmore than one electromagnetic end launcher 100 in an associated hollowwaveguide section 120. For example, two electromagnetic end launchers1010, 1020 may be provided in a single hollow waveguide section 1030,FIGS. 10A, 10B. Similar to the electromagnetic end launcher 100 of FIGS.1A-1C, each electromagnetic end launcher 1010, 1020 may includerespective ground posts 1014, 1024, center conductor transmission lines1015, 1025, and may also include respective longitudinally extendedportions 1012, 1022 of the center conductor transmission lines whichproject into the hollow cavity of the hollow waveguide 1030. A 16-waywaveguide power combiner/divider 1100 may then be provided using thedouble electromagnetic end launchers 1010, 1020 along with a 8-waywaveguide combiner 700 of the type shown in FIG. 7A, for example, FIGS.11A, 11B.

In another aspect of the present invention, any of the exemplarytransmission line output ports 330, 353, 730 make be configured tofurther communicate with a hollow output waveguide. For example, withreference to FIG. 12A the transmission line output port 1140 of awaveguide power combiner/divider 1200 may include a center conductortransmission line 1142 that has an upwardly extending portion 1143 whichmay be inserted into the hollow waveguide cavity of an output waveguide1180 to permit transmission of an RF signal present in the centerconductor transmission line 1142 into a radiation mode within the cavityof the hollow output waveguide 1180. Moreover, two waveguide powercombiner/dividers 1200 may communicate with a single hollow outputwaveguide 1280 to transmit respective output signals from a transmissionline to radiation modes of the hollow output waveguide 1280, FIG. 12B.Again, as mentioned from the outset the use of the termscombiner/divider or combine/divide depend on the manner in which theassociated device is used. Thus, if a radiation mode is fed as an inputto the hollow output waveguide 1280, the device of FIG. 12B wouldfunction as a divider.

While the exemplary configurations of waveguide power combiner/dividers500, 800, 900, 950, 1100, 1200 have been illustrated with feed throughelectromagnetic end launchers 100 in-plane and the transmission lineoutput ports 230, 730, 1140 perpendicular, other construction axes arepossible. For instance, similar performance may be possible whenincluding all inputs and outputs in one plane, all inputs and outputsorthogonal in at least one axis, and other various combinations andvariations. For example, electromagnetic end launchers 1310 of thepresent invention may enter a waveguide power combiner/divider 1300,1400 through an upper wall of the waveguide power combiner/divider 1300,1400, FIGS. 13A-14B.

In another of its aspects the present invention provides waveguide powercombiner/divider structures, such as those shown and described inconnection with FIGS. 1A-14B, implemented on a substrate including awafer containing active devices. A power combiner/divider SSPA 1500,1550 may include one or more drivers 1512, pre-drivers 1510, an N-wayinput power divider, such as a 4-way divider 1516 or cascading 2-waydividers 1518-1520, amplifier modules 1514, a microfabricated waveguidepower combiner/divider 800, and/or an air-coax or waveguide output 730.The length of a divider network, for example, an air coax dividerfeeding each amplifier module 1514, i.e., the dividers 1518-1520, may bethe same length in order to keep the same phase. N-way combiner/dividersmay be implemented using cascading 2-way splits, which can be done inboth waveguides with conducting transmission lines, such as coaxial orhollow core propagating mode waveguide structures, e.g., rectangularand/or folded hollow core waveguides, FIG. 17. The input power dividers1518-1520 may use an air-coax line or, a traditional transmission line(e.g. such as a microstrip or stripline), since the input network maynot be critical for power combining efficiency.

The power combiner/divider SSPA 1500, 1550 may include an air-coaxcombiner, phase shifters, filters and/or linearizers. Signals to beamplified may be fed from an input port 1501 through the circuit into aninput divider, for example a Gysel or Wilkinson 2-, 4-, or N-way dividerwhich may be based on waveguides such as micro-coaxial dividers. Thedivided signal may then be amplified using amplifier modules 1514 withthe output power from the amplifier modules 1514 transferred into amicrofabricated waveguide power combiner/divider 800 which mayincorporate an integrated means of producing a controlled alignment ofradiation modes in the waveguide combiner 800.

Because most of all power amplifier MMIC chips in SSPA 1500, 1550 may bemounted on the same base plate or by joining two assemblies, the heatgenerated by the MMICs can be dissipated through a heat sink with a lowthermal resistance to the chips, which can be mounted on the packagingof the system, which may achieve optimal thermal dissipation. A coolingsystem (e.g., such as cooling pipes or fins) may be integrated into thebase plate. Alternatively or additionally, a cooling gas or an inertcooling fluid may be applied within the module, the thermal base plate,or the heat sink. A sub-module may also be provided which may includemultiple MMIC chips that are combined with a low loss air-coax combinerand divider. The sub-module may be tested separately before the finalassembly and/or may be replaced for repairing. In addition, exemplaryMMIC chips may include a linearization circuit using pre-distortion orfeed-forward techniques and/or may use high isolation and low insertionloss switches in sections of the combiner or between stages of thecombiner circuit to allow regions to operate relatively independently ofother regions without suffering excess inefficiency in the amplifieroperating at different power levels. Signals from each channel may thenbe further combined to higher power levels in a reduced height waveguidecombiner and delivered to an air-coax or waveguide output. From a coaxoutput for example, the amplified signal can be transferred to astandard waveguide if a waveguide interface is desired.

In one exemplary configuration, the SSPA 1500, 1550 may be constructedfrom an upper assembly 1640 and a lower assembly 1650, SSPA 1600 FIG.16. The upper assembly 1640 may include amplifier modules 1614, and amicrofabricated waveguide power combiner 800. Amplifier modules 1614 maybe a MMIC such as a power amplifier MMIC, or may be themselves asub-module or assembly of chips, such as several amplifier MMICs. Morethan one type of MMIC or chip may be part of the modules 1614, forexample, a phase shifter and/or attenuator may be included before theMMIC power amplifier to adjust phase or power of the power amplifierMMIC or power amplifier transistors. The modules or subassemblies 1614may include a divider and combiner network as shown in FIG. 17, whichshows a 4-way and also an 8-way divider and combiner on the input andoutput ports of the amplifier chips shown in the middle. Such an outputcombiner network for the module 1614 may be made, for example, using amicro-coaxial combiner having the advantage of providing port to portisolation. The isolation may be achieved using a combiner structure suchas a Wilkinson or Gysel or other suitable transmission line powercombiner. Advantages of incorporating a combiner structure such as aWilkinson or Gysel in advance of the hollow waveguide combiner is thatthat in the event of single or multiple power amplifier MMIC failure orfailures, the increased isolation provided for each chip will preventreflected power from interfering with the other MMIC amplifier chips.This is because the reflected power can be absorbed by one or moreisolation resistors. Adding quadrature combining to these transmissionline combiner modules may further improve the match of MMIC poweramplifiers and can be incorporated. The lower assembly 1650 may includean input power divider network 1670 fabricated using traditionalstripline, microstrip, or micro-coax, or a waveguide divider, forexample. While loss is a primary consideration for the output powercombiner after the amplifier chips or chip modules 1614, the inputdivider may have higher insertion loss. The lower assembly 1650 may alsoinclude all the direct current (DC) routing (not shown), and the DClines may be shielded, for example by being separated by ground planes.A preamplifier may be made of one or two stages of amplifier chips orMMICs shown as 1610 and 1612. They may be integrated into lower assembly1650 and used to feed or drive the combiner upper assembly 1640. Theupper and lower assemblies 1640, 1650 may be configured to be joined tooperably interconnect the various components disposed thereon. Forexample, the lower substrate 1650 may include recessed areas or openings1660, 1662, 1664, 1668 to receive the pre-driver 1610, 1612, amplifiermodules 1614, and waveguide power combiner/divider 800, respectively. RFsignals running through the power divider network 1670 may be coupledinto the amplifier modules 1614 through respective input ports, as bestseen in the assembled SSPAs 1500, 1550 of FIGS. 15A, 15B.

One or more waveguide combiners may feed one or more waveguide combinersin series and/or parallel. They may combine one or more connectorstructures to interface to one or more input or output ports. They maybe made in a modular format to allow a product that can be scaled upwardor downward in power while still using similar components.

Another point to be appreciated from the dimensional simulations ofFIGS. 3A-3C, 8E is the importance of submicron dimensional and placementcontrol of the electromagnetic end launcher component structures (e.g.,structures 102-106, 120, 122) in the overall waveguide powercombiner/dividers of the present invention. Optimal launch performancemight only be achieved by a very tight control of the dimensions of thelaunch. This becomes even more critical as the frequency increases andthe size of the electromagnetic end launcher decreases. Thus, in anotherof its aspects the present invention relates to suitablemicrofabrication processes which permit the precision manufacturing ofsmall parts, typically on a wafer or grid-level or in a batch. Forexample, processes such as PolyStrata® processing, stereolithography, orsolid printing are suitable batch processes where the forming steps actin parallel on a number of parts to provide a sequential buildmanufacturing process.

Microfabrication is a manufacturing technology typically whereby thecombination of lithographic patterning combined with material additiveand/or material removal processes create 3D structures with precisiontypically in the microns to submicron scale. Often these additive orremoval processes are iterative and use one or more of vacuumprocessing, spin-coating, chemical, plasma, or mechanical processes andare applied across a mostly planar substrate surface in, or on, whichthe devices will be formed. Step-by-step the iterations typically createthe devices on a grid of regions on a surface. The devices are typicallyformed within, or on top of, substrates including but not limited tosilicon, glass, ceramic, and/or metal. For example, an 8″ diametersilicon wafer, similar to those used for making integrated circuits, isoften chosen for the wafer's flat surface and the ability for the waferto survive many additive and/or subtractive material processes withpatterning optionally at every layer. Typically, micro-fabricatedstructures are in the square mm size regime.

The waveguiding components of the waveguide power combiner/dividers andassociated componentry illustrated and discussed in connection withFIGS. 1A-17 may be monolithically formed together or may be separatelyformed in one or more parts and then may be integrated using alignmentstructures formed by the microfabrication process. Since theelectromagnetic end launchers together with waveguide powercombiner/dividers may be built by a consistent microfabrication process,optimized manufacturing repeatability and/or optimized performance maybe achieved at even higher frequencies. The PolyStrata® process enablessuch precision and therefore high quality performance. (The PolyStrata®process is disclosed in U.S. Pat. Nos. 7,012,489, 7,148,772, 7,405,638,7,948,335, 7,649,432, 7,656,256, 8,031,037, 7,755,174, and 7,898,356,the contents of which patents are incorporated herein by reference.)

A key difference between microfabrication methodologies and otherrelated precision machining techniques (laser drilling, precision CNC,electro-discharge machining (EDM)) is the parallel processing of manydevices at a time on at least one substrate (and usually more than onesubstrate) combined as well as the material complexity and diversitythat can be involved. For example, a device made of conductors,non-conductors, and containing multiple layers and enclosed regionscannot typically be formed with the precision or complexity using theaforementioned methods without some form of integration, alignment, andbonding. Compared to microfabrication, most types of precision machiningtypically process only one device at a time as opposed to many devicesproduced typically in layers in a batch. With microfabrication, theadditive or subtractive processes are applied across a whole substrate(with sometimes thousands of devices per substrate) at once. Thus,manufacturing of many devices with micron precision can be achievedrapidly with low labor content. Microfabrication has continued to emergeas a leading fabrication approach for future micro-mechanical andmicro-electro-mechanical devices.

In particular, the PolyStrata® process combines the option forprocessing of both metals and dielectrics in a micromachining technologyspecifically suited to the manufacture of devices of the presentinvention. The PolyStrata® process may be used to create air-dielectricmicrowave transmission components. The features of each stratum across awafer may be defined using photolithography. The x-y alignment fromlayer to layer may be done typically with ±2 μm in-plane accuracy, forexample, across a 50 mm, 100 mm, 150 mm, 800 mm, or 1200 mm substratesuch as a ceramic, SiC, silicon, copper, or stainless steel wafer.(While some materials have been named, alternative materials may besubstituted to produce structures with similar functions.) The wafermay, or may not, contain active devices in or on its surface some ofwhich may be designated to be in communication with the microstructuresto be built by the micromachining process. In the PolyStrata® process,once a pattern has been defined and developed over a region that isconductive, a photoresist, or molding material which may define thepattern, may be used as a mold for plating conductive features, e.g., ametal, such as copper. The copper may be planarized, for example, usinga chemical-mechanical polishing (CMP), lapping, turning, or acombination of these and/or similar methods. The mold material and thefill material such as copper may or may not be planarized simultaneouslyin one or more of these steps. At this juncture, photo-patternablepermanent dielectric supports, features, or sheets may be embedded inthe device or formed over or in the layer, or the photolithographyprocess begun anew, and the steps repeated. This process may continueuntil the entire height of the structure or structures being formed hasbeen achieved. The photoresist or mold material may then be dissolved toleave air-filled copper structures with dielectric supports for thecenter conductor. The resulting structures may have strata, or layers,of thicknesses from 5-100 μm. As such, exemplary structures disclosedherein having sufficient height requirements, such as for example groundposts 104, sidewalls of hollow waveguides 120, 250, transmission lineoutput ports 330, 350, and so forth, may be built layer-by-layer andcomprise a plurality of layers or strata.

In view of the foregoing, devices and methods of the present inventioncan be expected to provide advances in the art, such as: increasedfabrication speed, decreased cost, and increased ease to produce partsin large quantities over traditional machining of parts which requiretechniques such as EDM or laser processes; increased versatility inproducing complex geometries, especially 3D and enclosed geometries;lower loss at high frequencies due to improvements in parasitic effectsand substrate tangent loss; increased tolerance control based onmonolithic fabrication of electromagnetic end launchers with waveguidepower combiner/dividers, affording lower losses at high frequencies suchas at Ka-, V-, and W-band, with no need for adjustment or tuning of thepositions; increased room for a heat sink, which may improve thermaldissipation; and, reduction of phase and amplitude errors that reducethe combining efficiency.

These and other advantages of the present invention will be apparent tothose skilled in the art from the foregoing specification. Accordingly,it will be recognized by those skilled in the art that changes ormodifications may be made to the above-described embodiments withoutdeparting from the broad inventive concepts of the invention. It shouldtherefore be understood that this invention is not limited to theparticular embodiments described herein, but is intended to include allchanges and modifications that are within the scope and spirit of theinvention as set forth in the claims.

1. (canceled)
 2. A waveguide power combiner/divider for operation at aselected wavelength, comprising: a plurality of hollow waveguides eachhaving a hollow core configured to support at least one radiation modetherein; an output port in communication the plurality of hollowwaveguides to permit communication of radiation modes between the portand the hollow waveguides; and a plurality of transmission linewaveguides having a center conductor transmission line disposed therein,each of the transmission line waveguides having an electromagnetic endlauncher operably extending in to respective first ends of the pluralityof hollow waveguides.
 3. The waveguide power combiner/divider of claim2, comprising a plurality of ground posts each disposed at a respectiveend launcher in electrical communication with the center conductor and awall of the hollow waveguide, respectively, to ground the end launcherto the hollow waveguide wall.
 4. The waveguide combiner/divideraccording to claim 3, wherein the end launcher has a distal end andwherein the ground post is disposed inward from the distal end toprovide an overhang portion of the distal end.
 5. The waveguidecombiner/divider according to claim 3, wherein the sum of the length ofthe end launcher and the height of the respective ground post is about ¼of the selected wavelength.
 6. The waveguide combiner/divider accordingto claim 2, wherein the transmission line waveguides comprise a coaxstructure.
 7. The waveguide combiner/divider according to claim 2,wherein one or more of the hollow waveguides and transmission linewaveguides comprises a layered structure comprising a plurality oflayers.
 8. The waveguide combiner/divider according to claim 7, whereinthe plurality of layers of at least one of the hollow waveguides andtransmission line waveguides comprise the same material.
 9. Thewaveguide combiner/divider according to claim 2, wherein the pluralityof transmission line waveguides comprises two transmission linewaveguides operably connected to a respective first end of one of thehollow waveguides.
 10. The waveguide combiner/divider according to claim2, wherein the hollow waveguides are coplanar to one another and whereina longitudinal axis of the elongated center conductor is parallel to thecoplanar plane of the hollow waveguides.